1. Field of the Invention
The invention relates to control surface motion detection for maneuverable craft, particularly with respect to detecting the motion of the horizontal stabilizer of aircraft.
2. Description of the Prior Art
The horizontal stabilizer of modern jet transports is typically utilized in effecting pitch trim of the aircraft. The present day jet transport traditionally includes an automatic flight control system (AFCS) that includes an automatic pitch trim function. In such aircraft, it is necessary to provide the pilot with a warning indication when the rotational rate of the horizontal stabilizer exceeds a predetermined rate through a displacement in excess of a predetermined amount. Typically, the warning system is designed to detect when the horizontal stabilizer has travelled in excess of 1.degree. at a rate of greater than 0.08.degree. per second.
In the prior art, this function is performed in hardware. A shaft angle encoder coupled to the horizontal stabilizer shaft emits pulses as the shaft rotates at a pulse rate in accordance with the rotational rate of the shaft. A counter responsive to the pulses is maintained in a reset state when the pulse rate is less than 0.08.degree. per second. When the pulse rate exceeds 0.08.degree. per second, the reset is released permitting the counter to accumulate the pulses from the encoder. When the pulse count indicates that 1.degree. of motion has occurred since the rate exceeded 0.08.degree. per second, the apparatus effects the stabilizer motion warning. The warning may, for example, be provided to the central aural warning system (CAWS) of the aircraft instrumentation.
Generally, the prior art apparatus performs satisfactorily but requires expensive, bulky and heavy hardware to implement the function. Additionally, installation of the shaft angle encoder is a time consuming and expensive procedure requiring precision alignment. Since the prior art motion warning system is predicated on a mechanical device, the reliability thereof is undesirably low with a concommitant undesirably frequent maintainance schedule.